I was not very confident in this game going in. I had fond memories of failing at the original, so I picked it up day one. Needless to say I love the game.
Good:
1. Flying is incredibly fun
2. Charm- Voice acting is pretty great, and the script is strange and uniquely funny.
3. Ground levels present their own challenge and are often in very fun environments.
4. There are only 3 controls. Move, aim, and shoot. It works very well.
5. High replay value
6. Interesting difficulty meter allows you to bet on yourself. Think you can beat it on hard? You have to bet the in game currency you will. If you die you lose it all. If you succeed you gain access to special areas in the game and better weapons.
Bad:
1. Ground controls have a tough learning curve
Conclusion:
If you have a 3DS buy this game, I doubt anyone would advise otherwise. My current favorite for the system.